There is increasing need for an economical means for mass rearing of many lepidopteran species for commercial purposes.
Large numbers of larvae of various species are needed for the production of a variety of traditional biological control agents (predators, parasites, and parasitoids), which are taking on a greater importance in world agriculture. The sterile male technique for insect control requires economical production of great numbers of individuals for sterilization and release.
With the development of the baculovirus expression vector system [e.g., V. A. Luckow, "Cloning and expression of heterologous genes in insect cells with baculovirus vectors", In Recombinant DNA Technology and Applications, C. Ho. A. Prokop and R. Bajpai (eds.), pp. 97-152, McGraw-Hill, New York, 1990], insect larvae, principally lepidopterans, are being considered as a central part of systems for producing commercial quantities of many pharmaceutically important proteins.
Presently, insect viruses, primarily baculoviruses infecting lepidopterous pests, are being genetically engineered and developed as commercial biorational pesticides (H. A. Wood and R. R. Granados, "Genetically engineered baculoviruses as agents for pest control", Ann. Rev. Microbiol., 45: 69-87, 1991); the cost of their production is determined principally by the cost of rearing the insects used for their propagation.
Insects are even being considered as a valuable protein source themselves (e.g., "Eating bugs in the Big Apple", ESA Newsletter, 15(8), August 1992).
Current methods for rearing lepidopterous insects are extremely varied, depending on the species, the laboratory, and the purposes for which the insects are being reared. The two-volume series edited by Pritam Singh and R. F. Moore (Handbook of Insect Rearing, Volumes I and II, Elsevier Science Publishers, 1985), in which methods being used to rear 38 species of lepidopterans are described, is perhaps the most comprehensive treatment in recent years of methods for rearing these insects. In developing the invention described in this application, which particularly concerns the means by which the insects are reared from egg through the larval and pupal stages to adult, the cabbage looper, Trichoplusia ni, was used as a type species, and the many different methods that have been used for the mass-rearing of this species are typical of those used for lepidopterans in general [for reviews see: N. C. Leppla, P. V. Vail, and J. R. Rye, 1984, "Mass Rearing the Cabbage Looper, Trichoplusia ni", In Advances and Challenges in Insect Rearing, E. G. King and N. C. Leppla (eds.), U. S. Dept. Agric. Tech. Bull. pp. 248-254 ; R. H. Guy, N. C. Leppla, J. R. Rye, C. W. Green, S. L. Barrette, and K. A. Hollien In Handbook of Insect Rearing, P. Singh and R. F. Moore (eds.), Vol. II, 1985, pp. 487-497].
A great variety of containers have been used for the larval stage. P. V. Vail, S. J. Anderson and D. L. Jay ("New procedures for rearing cabbage loopers and other lepidopterous larvae for propagation of nuclear polyhedrosis viruses", 1973, Environ. Entomol. 2, pp. 339-344) described the use of paraffin-coated paper bags (16.times.19.5.times.32 cm deep) with 500 ml of diet and 250 eggs/bag yielding 190 pupae; these bags were hand-coated with paraffin and the thickness of the coating was critical to their success (the diet "sweated excessively" if the coating was too thick and dried excessively if the coating was too thin). The most frequently used type of larval rearing container has been paraffin-coated paper cups. T. J. Henneberry and A. N. Kishaba ["Cabbage Loopers", in Insect Colonization and Mass Rearing, C. N. Smith (ed.), Academic Press, 1966, pp. 461-478] described the use of 6- or 8-oz (ca. 178 to 237 ml) cups for rearing the larvae to pupation and recommended a maximum of 24 larvae/cup with 70-80 ml of diet. Such cups were used in a small-scale virus production plant described by F. R. Lawson anti R. L. Headstrom ("Small plant for production of Trichoplusia ni NPV", In Facilities For Insect Research and Production", N. C. Leppla and T. R. Ashley (eds.), U.S. Dept. of Agric. Tech. Bull. 1576, 1978, pp. 37-39. Plastic containers (30.5.times.30.5.times.12.7 cm deep I.D.) were described for rearing the larvae by R. H. Guy, N. C. Leppla, J. R. Rye, C. W. Green, S. L. Barrette, and K. A. Hollien ["Trichoplusia ni", In Handbook of Insect Rearing, P. Singh and R. F. Moore (eds.), Vol. II, 1985, pp. 487-497]; each of these containers was seeded with 300-350 eggs with 1 liter of diet and yielded ca. 240-280 pupae.
When the insects have pupated in the cups, the pupae are typically removed by hand, subjected to a surface-sterilization procedure, and placed into some type of emergence cage distinctly different from the larval rearing container. For example, Henneberry and Kishaba collected the pupae from the larval rearing cartons, soaked them for 10-15 minutes in 1-1.5% sodium hypochlorite, rinsed them several times in tap water, placed then, on paper toweling to dry, and then placed them in emergence cages made from 1-gal cylindrical cardboard containers. The method of Guy et al. contained the same steps with the addition of using forceps to remove all debris after the pupae dried, counting the pupae, and weighing a random sample.
The cost associated with most commercial uses of lepidopterous larvae, such as production of viruses, parasites, etc., is largely that of rearing the larvae. The above methods generally are too costly to make the products commercially practical and/or economically competitive with other options in the present-day market. They typically require 3-4 ml of diet/starting individual insect and require a high amount of area per initial insect and/or have low yields of late instars (e.g., 35 cm.sup.3 /starting individual and 80% yield by the method of Guy et al. or 40 cm.sup.3 /starting individual and 76% yield by the method of Vail et al.). Also, a considerable amount of labor is required through the complete rearing cycle, such as handling large numbers of small rearing units (i.e., cups), collecting and sterilizing pupae, and transferring pupae into emergence cages. Furthermore, considerable difficulty has been encountered in controlling the moisture/humidity in the rearing containers, especially creating problems with controlling fungi and bacteria.